This invention relates to methods of flocculating particulate solids suspended in aqueous media.
In the processing of mineral ores, coal and other industrial slurries, it is often necessary to flocculate suspended solids from aqueous media, and in particular, acidic aqueous media. For example, in the case of mineral ores and coal containing materials, it is often desirable to subject such ores and coal products to an acid treatment or an acid leaching or acid digestion step in order to facilitate the separation of the mineral or coal values from the unwanted clays, sand and other finely divided solids. Such acid treatment steps often generate suspensions of finely divided solids in acidic aqueous media from which solids must be flocculated before further processing can occur or the liquid media can be discharged, recycled or used. Conventionally, such flocculation is accomplished by contacting the suspension with a water-soluble copolymer of acrylamide and acrylic acid or acid hydrolyzed polyacrylonitrile as described in British Pat. No. 760,279 and U.S. Pat. No. 3,418,237. Unfortunately, these polymers, i.e., the nonionic polyacrylamide and the anionic copolymers of acrylamide and acrylic acid are not as effective in flocculating suspended solids from acidic aqueous media as is desired.
More recently, the use of anionic polymers has been disclosed as being effective in flocculating various systems as is described in U.S. Pat. Nos. 3,717,574 and 4,342,653. However, the methods of flocculation taught in said patents are not as effective in providing supernatant liquids of high clarity (i.e., free of fine particulate matter) as is desirable. That is, due to the nature of impurities such as fine amorphous silica particles and low pH colloids, the clarity of the supernatant liquids is poor.
The use of an amount of anionic polymer containing a carboxylic acid, a carboxylic acid anhydride and a carboxylic acid salt; and a cationic polymer to remove coal fines and clay from an aqueous suspension is disclosed in U.S. Pat. No. 3,408,293. Unfortunately, such a combination provides a method for clarifying systems exhibiting a limited pH range. In addition, such a combination requires careful control of amounts of polymers employed and of settling rates of flocculated particles.
In view of the deficiencies of the prior art, it would be highly desirable to provide an improved method for flocculating suspended solids from aqueous media which is effective in providing a supernatant liquid having improved clarity.